Why compare to the E90 M3? It will share close to nothing with the F80. Forget that and focus on the F30 335i. It is much more similar in size and engine configuration and will share some parts. This is the car you should start out with and look at what can be done to reduce weight. The F30's chassi needs to be cheap enough to be used with profit for the entry level 3. The F80 has no such restriction. It will start at a price point way above the 335i. There is a LOT of room to add cost to the F80 chassi compared to the F30.

Way too much negative thinking in terms of weight. It's understandable though since BMW has been on a pretty constant disappointment streak lately. Just another reason why they will be willing to spend to make the F80 brilliant.